During winter or on a rainy day, frost is formed on a glass surface of a vehicle because of a difference between temperatures of the outside and inside of the vehicle. In addition, in the case of an indoor ski resort, a dew condensation phenomenon occurs because of a difference between temperatures of the inside where there is a slope and the outside of the slope. Heat emitting glass has been developed in order to solve the problem. The heat emitting glass is a notion that after a thermal conductive layer or hot wire pattern is formed on a surface of glass, heat is generated by applying electricity, thereby increasing a temperature of the surface of glass.
In particular, it is important for the heat emitting glass for a vehicle to have low resistance in order to generate sufficient heat, and, more importantly, the heat emitting glass should not be unpleasant to the human eyes. Accordingly, a method for manufacturing the heat emitting glass through ITO (Indium Tin Oxide) sputtering has been tried. However, in this case, there is a problem in that heat is not sufficiently emitted.
A hot wire may be used as a method for constituting the heat emitting glass. In this case, if the hot wire is constituted by being arranged in a constant pattern such as a triangular or trapezoidal form according to the form of glass, a portion where a distance between bus bars is changed may be generated.
If the distance between the bus bars is changed, a resistance value of the hot wire is changed according to the distance between the bus bars. Furthermore, a value of a current flowing in each hot wire in the bus bars under a predetermined voltage is changed, such that heat is not uniformly emitted.
As described above, in the case where the distance between the bus bars is changed according to the form of glass, the following two methods are used in order to implement a uniform heat emitting level.
First, there is a method for controlling an emission level of heat provided per area by controlling a thickness of a hot wire and a space between the hot wires. Second, there is a method for implementing uniform heat emitting by disposing all the bus bars of two electrodes at a lower end, and changing a thickness of a hot wire according to a change in length of the hot wires connecting both bus bars.
The above two methods can ensure a predetermined level of a uniform heat emitting property. However, since a distribution of areas occupied by the arranged hot wires, that is, a density of the hot wires per unit area is changed according to the position, it is impossible to implement a uniform pattern arrangement. For example, in the case of glass for a vehicle, when a driver in the vehicle observes the outside through the glass for the vehicle, a recognition property of a hot wire pattern is increased due to a non-uniform distribution of the hot wire pattern, such that there is a problem in that a field of vision of the driver may be obstructed.